The present invention relates to a solar radiation sensor apparatus, and more specifically relates to improvements in the sensitivity characteristic with respect to the incident angle (hereafter referred to as "the incident angle sensitivity characteristic") of a solar radiation sensor apparatus in which a photoelectric element such as a photodiode is employed and which may be used in an automatic air conditioner of a vehicle.
A conventional solar radiation sensor apparatus in which a photoelectric element such as a photodiode is employed has an arrangement provided for the purpose of improving incident angle sensitivity characteristics. For instance, a plurality of photoelectric elements are used, as disclosed in Japanese Utility Model Unexamined Publication No. 58-36912, or a light attenuating filter provided for achieving a non-uniform distribution of the light transmittance is disposed above the light-receiving surface of the photoelectric element, as disclosed in Japanese Patent Unexamined Publication No. 61-210915.
According to the prior art disclosed in Japanese Utility Model Unexamined Publication No. 58-36912, however, since a plurality of photoelectric elements are used, the solar radiation sensor apparatus has increased external dimensions, while making production cost several times higher than before. According to the prior art disclosed in Japanese Patent Unexamined Publication No. 61-210915, since the light attentuating filter must have a diameter between 25 to 30 mm, the solar radiation sensor apparatus has increased external dimensions. In this way, either of the systems an and an increase in production cost.